The present invention relates to the reaction of hydrogen gas with titanium-based metal alloys, and particularly to the rapid reaction at mild temperatures of hydrogen gas with solid solution alloys having a body-centered cubic phase structure comprising titanium and a second metal selected from a group consisting of molybdenum, vanadium, and niobium and dissolved in the binary alloy having said body-centered cubic phase structure wherein said second metal is vanadium or niobium and optionally molybdenum at least about 1 atom percent of a third metal such as aluminum, cobalt or iron.
Most metals that form hydrides react very slowly in bulk form at room temperature with hydrogen gas. Metallic niobium and metallic vanadium, for example, are relatively inert in bulk form at room temperature in the presence of hydrogen gas, with the hydrogen only slowly reacting with the body-centered cubic phase structure of each metal to form a precipitated niobium hydride or vanadium hydride. Most other metals that form hydrides react in a similar fashion, with the rate of alpha phase formation and hydride formation varying among metals and alloys, but rarely occurring at room temperature in less than one hour. In the case of niobium, attempts to increase this rate by plating over niobium with nickel or palladium or iron have been reported.
Metallic titanium is also relatively inert in the bulk form at room temperature in the presence of hydrogen gas with hydrogen dissolving only slowly reacting with hexagonal close packed phase structure of metal to form a precipitated titanium hydride.
For many applications of metal hydrides, such as hydrogen recovery, it is desirable to form the hydride from bulk metal, pulverize the hydride into some form of granular or powder structure, and thereafter cyclically remove hydrogen to form a lower hydride or the free metal and thereafter reintroduce hydrogen to reform the hydride. Starting with bulk metal or bulk alloy, it is normally necessary to go through an induction period, wherein the metal is heated to a temperature such as 300.degree.-700.degree. C., then reacted with hydrogen at high pressure and then cooled very slowly until a temperature below about 100.degree. C., and preferably about room temperature, is reached. At the higher temperature, the rate of hydrogen dissolving in the metal (the alpha phase) is increased so as to achieve saturation in a matter of minutes rather than hours or days. At the high temperature, however, the equilibrium hydrogen pressure is so high that relatively little hydrogen actually dissolves or forms hydride. Accordingly, it is only upon gradual cooling that hydrides form. See, for example, U.S. Pat. No. 4,075,312 (Tanaka et al.) which discloses titanium alloy hydride compositions containing at least one metal selected from the group consisting of vanadium, chromium, manganese, molybdenum, iron, cobalt, and nickel.
J. J. Reilly et al. (Inorganic Chemistry, 1974, vol. 13 at page 218) discloses that intermetallic compounds of iron and titanium, FeTi and Fe.sub.2 Ti form iron titanium hydrides. U.S. Pat. No. 4,318,897 (Gonczy) discloses ferrovanadium alloys containing from about 5 to about 30% by weight iron may be used for hydrogen storage systems.
J. F. Lynch et al. in Advances in Chemistry 1978, vol. 167, pages 342-365 discloses that titanium-molybdenum alloys are useful for hydrogen isotope separation. In all these disclosures, an initial induction period at a high temperature in the presence of hydrogen is required for hydride formations.
While many metals require only a single induction process to form the hydride, with the subsequent hydride powder cycling at a reasonable reaction rate, it should be apparent that the induction process represents a distinct disadvantage in forming and utilizing metal hydrides.